1. Field of the Invention
The present invention generally relates to an electrically tunable optical phase modulation element, and in particular, relates to an electrically tunable optical phase modulation element that can provide smoother electrical field distribution and better lens quality.
2. Description of Related Art
Electrically tunable optical phase modulation can be achieved by using a variety of methods, such as through liquid lenses, deformable mirrors, or gradient refractive index lens (GRIN lens). Out of these different methods, electrically tunable GRIN lens has gained a lot of interest due its light and thin structure.
In general, electrically tunable GRIN lens has the basic structure whereby a layer of optoelectronic materials is disposed in between the upper and lower substrate. The optoelectronic materials used are such as liquid crystal materials that may have different refractive index changes when applying different voltages. Through the design of electrodes on the substrates and by applying specific voltages, a phase difference distribution of the optoelectronic material layer can be made to imitate a non-uniform electrical field equivalent to that of a normal lens. However, there are still many drawbacks in the current design of electrodes for generating the non-uniform electrical field. For example, in stripe electrodes where the electrodes extend along the X-Y direction, the electrical field is not smoothly distributed, such that the phase difference may change step by step in a ladder shape form, hence affecting the quality of the lens. As such, there is a need to eliminate a grid like electrical field generated in conventional electrically tunable lens caused by the unsmooth distribution of the phase difference.